One idea it tried in its early days is classifieds ads. Now Facebook is reviving that experiment, with the project on a "fast track," according to The Daily.

The ads would charge people a small fee for prominent placement in friends' news feeds. That's similar to a controversial service Facebook recently introduced where individuals can pay to boost the visibility of their posts.

People could post roommate-wanted ads, and tag friends they might think they're interested, for example.

Will this mean Facebook could steal some of LinkedIn's recruiting-ads business? Possibly. Facebook has a huge advantage in the number of people it reaches. But startups that have tried to build LinkedIn-like professional networks on top of Facebook have run into a fundamental problem: People don't put a lot of career-related information on their Facebook profiles.

LinkedIn has done a far better job of encouraging people to put career details, skills, and other relevant professional information on its site. So job ads that target people based on the information they put on Facebook may miss a lot of promising candidates.

If Facebook wants to get into the recruiting-ads business in a serious way, it will need to figure out how to change its users' behavior when it comes to sharing professional information.